A biophysical investigation on the binding and controlled DNA release in a cetyltrimethylammonium bromide-sodium octyl sulfate cat-anionic vesicle system

The interactions between cat-anionic (an acronym indicating surfactant aggregates (micelles and vesicles) formed upon mixing cationic and anionic surfactants in nonstoichiometric amounts) vesicles and DNA have been the subject of intensive studies because of their potential applications in biomedicine. Here we report on the interactions between DNA and cetyltrimethylammonium bromide (CTAB)-sodium octyl sulfate (SOS) cat-anionic vesicles. The study was performed by combining dielectric relaxation spectroscopy, circular dichroism, dynamic light scattering, ion conductivity, and molecular biology techniques. DNA is added to positively charged vesicles until complete charge neutralization of the complex and formation of lipoplexes. This occurs when the mole ratio between the phosphate groups of DNA and positive charges on the vesicle is about 1.8. Above this threshold the nucleic acid in excess remains free in solution. This very interesting new result shows that anionic surfactants are not expelled upon saturation, and therefore, no formation of micelles occurs. Furthermore, vesicle-bound DNA can be released in its native form, as confirmed by dielectric spectroscopy and circular dichroism measurements. The nucleic acid is released upon addition of SOS, which competes with the phosphate groups of the DNA: this results in the demolition of the CTAB-SOS cat-anionic vesicles. These results indicate the possibility of a controlled DNA release and might be of interest in biomedicine.